General News

When the air is full of water

In many manufacturing units compressed air is an essential source of power, and the quality requirements of the compressed air are often sky-high. Even if the air leaving the compressor station meets all requirements, it can absorb more condensation than what is acceptable on its way through the pipelines in the factory. This water is definitely not desirable in the production machinery. In fact, the condensation was a significant problem for the valve production in Nordborg - without quite knowing how to solve the problem. The simple solution turned out to be a refrigerated air dryer

By Helle Friemann Nielsen
Valves are produced in Nordborg, Als. Actually, a lot of valves.
In department L3, where Danfoss A/S is producing its cooling valves, an average of 50,000 valves in a long line of different variants and materials are made each week. It is therefore of utmost importance that the production facility operates without any significant problems or interruptions.
A large part of the work stations in L3 are pneumatically operated. The compressed air is used to activate valves, as well as open/close functions. The air is therefore an essential supply source, and Danfoss has sky-high quality standards for the compressed air.

Problems with condensation
Danfoss' L3 has a large subterranean compressor station, which delivers compressed air of the highest quality. Yet there were still problems with condensation in the compressed air. Not when the air left the compressors - but afterwards as the air passed through the supply pipes to the individual stations.
"We could actually see how the water sat in the pipes", says Jytte Petersen, who is a purchaser for L3 and has an extensive knowledge of the techniques and production involved. She had worked for 10 years in maintenance and repair, before taking over the role of purchaser 12 years ago.
"I certainly do know how things work."
It was a big problem that the water was carried with the compressed air to the production systems, where the water caused significant damage to the valves, cylinders, fittings, etc. The components rusted and the water rinsed out the lubrication significantly shortening their life span.
"One thing was significantly shorter service life spans for these components - yet another was the drop in task times for each work stations. In other words, that made our production slower." "In addition we experienced the grippers suddenly started losing things," she adds and continues:
"Moreover, there were problems starting up, if for example, production had been shut down over the weekend. It required a little detective work in the morning to get the individual work stations up and running. Something with 'wiggling' the valves a little bit, repeating the start up, and so on."
"We simply had no idea how we could solve the problem, because the compressed air was of the highest quality, so there was nothing else that could be done. We lived with the problem, and physically drained the water out of the pipes, as well as replaced valves and other components here and there when they gave out," states Jytte Petersen.
"We joked about having ghosts in the machines, because there were no logical explanations for the numerous 'funny and puzzling' faults that constantly appeared.

A bit of a coincidence
It was actually a little bit of a coincidence, that the solution to the problem was found.
SMC Pneumatik A/S, which has been a supplier for Danfoss for many years, was visiting for unrelated reasons and by coincidence, the conversation came upon the water problem.

SMC had the answer.
The solution was very simple and is now implemented in 12-15 machine stations around L3.
"The solution was simply a refrigerated air dryer," says Ole Gert Jørgensen, who is the technical executive for SMC Pneumatik A/S.
The refrigerated air dryers are physically placed on top of those machines, where the compressed air enters the machine. The compressed air is led through the refrigerated air dryer, which cools the air - whereby the air is dried, and the water content is drastically reduced.
"Not all machines have a refrigerated air dryer. They are, in principle, located on the most critical work stations in the production, and on the first machine on the compressed air outlet pipe. The machines, which are connected to the same pipe also receive the dry, clean air," adds John Svendsen, who is a sales consultant with SMC.

Cause and mode of operation
"The reason why the compressed air releases condensation on its way through the supply pipes in the production, is for a start that it cools down on the way. It can, for example, also be due to operational stop in the compressor room's refrigerated air dryers or the conditions of the pipe and lack of ability to drain the pipes. Another cause is, when the air is transported through the pipes, high velocities can occur in bends and couplings between smaller and larger pipes - and here the water vapour condenses to water," explains Ole Gert Jørgensen.
The air's relative humidity is normally 65% - of course depending on the temperature and humidity.
It is impossible to produce compressed air without depositing water in the system, and a way to remove that water is needed. The best method is to chill the air and drain, whereby the water content is naturally reduced.
"There is less water in cold air than in warm air," asserts Ole Gert Jørgensen.
The refrigerated air dryer works by chilling the air to 3°C (from around 19°C in the supply pipes). Thereby reducing the water content in the compressed air from 18 grams per cubic meter to six grams. The surplus 12 grams of water is drained directly from the refrigerated air dryer, and practically speaking the water is tapped to a bottle under the machine.
"We still tap water as before, but now in much smaller amounts, plus it is very controlled and regular," says Jytte Petersen.
In short the water rich compressed air is fed into the refrigerated air dryer and is chilled with a heat exchanger. Condensation is removed by cooling and is drained automatically. The now cool, dry air is warmed afterwards and led out of the refrigerated air dryer.
"Therefore there will also be a difference in the water content during the summer and during the winter. The air is warmer during the summer and absorbs more condensation. During the winter, when the air is naturally much cooler, the air contains less water.

A time before and after the refrigerated air dryers
"There was a world of difference in our daily life after the refrigerated air dryers were installed," says Jytte Petersen and adds:
"All of the 'funny' ghosts in the machines have disappeared - and we no longer use our mornings on locating faults and detective work. The machines start exactly as intended.
"From a strictly cost point of view it is also clearly different case. Before, we replaced valves, cylinders and so on, here and there, because they suddenly gave up. We no longer do that. Before on a yearly basis we replaced in the region of 125 valves a year, which came to an amount of around 90,000 DKK Now, I believe, we replace five pieces due to normal wear and tear," she states.
In addition, replacing parts isn't just a question about the price of the valve: The entire work station needs to be shut down - and stoppages are as know expensive."
"An item in the budget, which has changed notably since the refrigerated air dryers were installed, is the total man hours used on tracing faults and maintenance. Earlier it was a pretty large item. It no longer is," says Jytte Petersen.
And she is supported by service men on the floor responsible for the machines. They can certainly see a clear difference in the daily work routine.